Pressure-induced phosphorescence enhancement and piezochromism of a carbazole-based cyclic trinuclear Cu(i) complex

Article abstract of DOI:10.1039/d0sc07058k

Interest in piezochromic luminescence has increased in recent decades, even though it is mostly limited to pure organic compounds and fluorescence. In this work, a Cu₃Pz₃(Cu₃, Pz: pyrazolate) cyclic trinuclear complex (CTC) with two different crystalline polymorphs, namely1aand1b, was synthesized. The CTC consists of two functional moieties: carbazole (Cz) chromophore andCu₃units. In crystals of1a, discreteCz-Cu₃-Cu₃-Czstacking was found, showing abnormal pressure-induced phosphorescence enhancement (PIPE), which was 12 times stronger at 2.23 GPa compared to under ambient conditions. This novel observation is ascribed to cooperation between heavy-atom effects (i.e., from Cu atoms) and metal-ligand charge-transfer promotion. The infinite π-π stacking ofCzmotifs was observed in1band it exhibited good piezochromism as the pressure increased. This work demonstrates a new concept in the design of piezochromic materials to achieve PIPEviacombining organic chromophores and metal-organic phosphorescence emitters.

Full text of DOI:10.1039/d0sc07058k

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Pressure-induced phosphorescence enhancement
and piezochromism of a carbazole-based cyclic
trinuclear Cu(I) complex†
Cite this: Chem. Sci., 2021, 12, 4425
All publication charges for this article
have been paid for by the Royal Society
of Chemistry
a
b
a
a
c
c
Mo Xie,
Xiao-Ru Chen, Kun Wu,
Zhou Lu, ‡ Kai Wang,
Nan Li,
*
a
b
a
c
Rong-Jia Wei,
Shun-Ze Zhan,
Guo-Hong Ning, * Bo Zou
and Dan Li *a
Interest in piezochromic luminescence has increased in recent decades, even though it is mostly limited to
pure organic compounds and fluorescence. In this work, a Cu Pz (Cu , Pz: pyrazolate) cyclic trinuclear
complex (CTC) with two different crystalline polymorphs, namely 1a and 1b, was synthesized. The CTC
consists of two functional moieties: carbazole (Cz) chromophore and Cu units. In crystals of 1a, discrete
Cz–Cu –Cu –Cz stacking was found, showing abnormal pressure-induced phosphorescence
3
3
3
3
3
3
enhancement (PIPE), which was 12 times stronger at 2.23 GPa compared to under ambient conditions.
This novel observation is ascribed to cooperation between heavy-atom effects (i.e., from Cu atoms) and
metal–ligand charge-transfer promotion. The infinite p–p stacking of Cz motifs was observed in 1b and
it exhibited good piezochromism as the pressure increased. This work demonstrates a new concept in
the design of piezochromic materials to achieve PIPE via combining organic chromophores and metal–
organic phosphorescence emitters.
Received 28th December 2020
Accepted 27th January 2021
DOI: 10.1039/d0sc07058k
rsc.li/chemical-science
19,20
induced emission (AIE) effect.
To date, the molecular
Introduction
design and material selection for piezochromism are mostly
Because of the weak spin-
which exhibit signicant emission orbital coupling and a long triplet-state lifetime, the pure
21–25
Piezochromic luminescent compounds are a class of stimuli- focused on organic molecules.
responsive materials
colour changes in response to grinding, pressing and stretch- organic molecules hardly show phosphorescence at room
1,2
26,27
ing, and they show great potential in a wide range of applica- temperature (rt).
Thus, most of piezochromic luminescent
tions, including pressure sensors, optical recording, and materials display a pressure-induced uorescence change at rt
3
–10
memory.
of such materials are related to pressure-controllable molecular hypsochromic shis),
Recent studies revealed that chromic mechanisms (e.g., quenched or enhanced intensity and bathochromic/
5,12,20
whereas pressure-induced phospho-
conformational trans- rescence enhancement (PIPE) materials are highly challenging
1
1–13
14,15
switches,
phase transition,
16,17
18
formation,
excited state transformation, and aggregation- and still remain unexplored.
1
0
Cyclic trinuclear complexes (CTCs) with d metals are well
known for their characteristic M
6ꢀx (M ¼ Au, Ag, or Cu; x ¼
, 3, or 6) nine-membered ring and corresponding p-acidity/
3 x
N C
a
College of Chemistry and Materials Science, Guangdong Provincial Key Laboratory of
Functional Supramolecular Coordination Materials and Applications, Jinan
University, Guangzhou, Guangdong 510632, People's Republic of China. E-mail:
guohongning@jnu.edu.cn; danli@jnu.edu.cn
0
basicity, and metal–metal interactions (metallophilicity) which
play essential roles in photoluminescence (PL) and other prop-
2
8,29
b
Department of Chemistry, Shantou University, Shantou, Guangdong 515063, People's erties.
Republic of China
In cooperation with other supramolecular interactions
30
(non-covalent interactions), such stimuli-responsive lumines-
c
State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012,
cence has oen been reported in the CTC family, including pie-
People's Republic of China. E-mail: zoubo@jlu.edu.cn
31
32–34
zochromism,
thermochromism,
solvatochromism, and
†
Electronic supplementary information (ESI) available: Experimental and
3
5
concentration luminochromism. In previous studies, phos-
phorescence of organic chromophores could be triggered at
calculation details; general characterization data, including IR, PXRD, and TGA;
crystal data and structure renement parameters; UV-vis spectra;
varied-temperature solid-state emission spectra; detailed photophysical data cryogenic temperatures or even at rt, aer forming CTC/organic
2
8,36,37
and proposed Jablonski diagrams; linear relationships; detailed TDDFT results; adducts or if directly serving as ligands.
Such lumines-
and pressure-dependent simulation results. CCDC 2043666–2043668. For ESI
cence, termed “metal-sensitized phosphorescence”, is attributed
to the enhanced intersystem crossing (ISC) rate from singlet
excited states to triplet states mediated by an external heavy-atom
and crystallographic data in CIF or other electronic format see DOI:
1
0.1039/d0sc07058k
‡
Present address: Department of Chemistry, University of North Texas, Denton,
38,39
effect (e.g., Au, Ag, Cu and Hg).
In this way, it is proposed that
Texas 76203, USA.
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Cu
3
Pz
3
CTCs (Cu
3
Pz: pyrazolate) with a non-conjugated exible
n-butyl chain. Two crystalline polymorphs, denoted as 1a and
b, are obtained and exhibit two different stacking models
leading to the formation of [Cz–Cu –Cu –Cz] excimers and Cz
1
3
3
excimer/aggregator, respectively (Scheme 1). Therefore, metal-
sensitized phosphorescence and the ligand-dominated lumi-
nescence are observed for 1a and 1b, respectively. Furthermore,
1a shows an unprecedented PIPE phenomenon, which has
never been reported in piezochromic materials, and 1b exhibits
conventional carbazole characteristic piezochromic lumines-
cence with a good linear relationship of intensity versus external
pressure.
Results and discussion
Scheme
stacking of two crystalline polymorphs 1a and 1b, and the formation of
the Cu Pz CTC Cz–Cu –Cu –Cz excimer and carbazole (Cz) exci-
1 A schematic representation showing the molecular
The yellow block-shaped crystals of 1a, or colourless brous
crystals of 1b were obtained by mixing 9-(4-(3,5-dimethyl-1H-
3
3
3
3
pyrazol-4-yl)butyl)-carbazole ligand (HL) and Cu
drous ethanol or ethanol/water under solvothermal conditions
see ESI† for further details). The freshly synthesized single-
2
O in anhy-
mer with an increase in pressure.
(
crystal samples of 1a and 1b were characterized by powder X-
ray diffraction (PXRD) and infrared (IR) spectroscopy, con-
the external isotropic pressure can enforce the interactions
between CTCs and organic chromophores, resulting in alteration
of electronic structures of the emission centre and triggering the
PIPE. As far as is known, investigations of the luminescence
behaviour of such organic chromophore-CTC adducts under
high pressure have rarely been reported.

rming their phase purity (Fig. S7 and S8, ESI†). The single X-
ray crystallographic analysis of 1a and 1b revealed that both
featured the nine-membered Cu N CTC composed of Cu units
3 6 3
and Cz motifs (Fig. 1a and 2a).
Unlike the conventional sandwich-like ternary adducts (i.e.,
In this work, a carbazole-based Cu(I) CTC (1) was designed by
41,42
40
CTC–organic aromatic–CTC),
unprecedented discrete
linking classic organic chromophore carbazole (Cz) and
adducts with a Cz–Cu –Cu –Cz stacking model were observed in
3
3
3 3
Fig. 1 (a) The crystal packing of 1a at 100 K, showing discrete Cz–Cu –Cu –Cz stacking (Cu: brown, C: grey, and N: blue, H atoms are omitted
for clarity). Emission spectra of 1a at a range of external pressures from (b) 1 atm–2.23 GPa and (d) 2.23–12.16 GPa at an excitation wavelength of
2
2
3
55 nm. The curve fitting [function: y ¼ A
1
ꢁ exp(ꢀx/t
1
) + y
0
, R ¼ 99.32%] and linear fitting [function: y ¼ A
0
+ kx, R ¼ 96.39%] of pressure and PL
intensity for 1a in pressure ranges of (c) 1 atm–2.23 GPa and (e) 2.23–12.16 GPa (insets of (c) and (e): PL photographs at representative pressure
points).
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dominant in the S14 state (Table S4, ESI†). These results sug-
1
gested that 1a will produce LC uorescence upon LE excitation
to the S –S states. By exciting 1a to the S14 or higher energy
1
13
singlet states by increasing excitation energy, the ISC process
might be generated by metal copper participation. The Cz–Cu
Cu –Cz stacking model of 1a is divided into two theoretical
models for clarity, denoted as dimer (a) or (b), which contained
Cu –Cu dimers or Cu –Cz adducts, respectively. The lowest
3
–
3
3
3
3
single–triplet excited states of both monomer and dimer (a)
were localized on the Cz moieties (Table S5, ESI†), which can be
assigned as metal-sensitized ligand centred (MSLC) phospho-
3
3
rescence. The charge transfer ( LC/ MLCT) excited state based
on the Cu –Cz interaction contributed a little (9%) to the triplet
emission of dimer (b), suggesting that the copper metal directly
3
Fig. 2 The PL spectra and photographs of 1a in a pressure relief participated in the triplet electronic transition rather than just
process from 2.28 GPa to 0.00 GPa. The gray line (marked as 1 atm) is sensitizing the LC emission. Therefore, the LE dual emissions
the PL spectrum before compression.
3
of 1a can be assigned as the LC of the monomer (lem ¼ 560 nm)
3
and the domination of the MSLC mixed with the MLCT
assisted phosphorescence of the Cz–Cu –Cu –Cz excimer (lem-
3
3
1
3
a (Fig. 1a). Specically, two adjacent Cu units adopted
¼
680 nm). Taking advantage of the Cu –Cz interactions, the
3
a dimer-of-trimer conguration with short intertrimer dCu/Cu
of 2.854 and 2.909 A, implying that there were strong Cu/Cu
interactions between the Cu3 units. Moreover, one set of Cz
groups adducted with the Cu –Cu dimer and the intermolec-
ular plane-to-plane distance between the Cu unit and the Cz
group (dCu /Cz) was 3.360 A, which indicated weak p-acid/
base interactions (Fig. 1a). It is worth noting that the other Cz
groups were randomly arranged and no noticeable interactions
heavy atom effects of copper atoms promoted the ISC rate and
the generation of low-energy phosphorescence, leading to
MSLC phosphorescence dominated emission of 1a. The
proposed complete photophysical processes are summarized in
Fig. S23 (ESI†).
ꢀ
3
3
3
ꢀ
3
It is known that pure carbazole possesses excellent piezolu-
40
minochromism. The unique mixed MSLC/MLCT phospho-
rescence of Cz-based CTC 1a promoted further study of the PL
between Cu
a exhibits a UV-vis absorption prole similar to that of the
proligand HL in either CH Cl solution or solid state (Fig. S14
3
or Cz units were observed (Fig. S10 and S11, ESI†).
under high pressure. The isotropic hydrostatic pressure was
1
43
directly applied via a diamond anvil cell (DAC) on crystal
2
2
samples of 1a (see ESI† for experimental details). At ambient
conditions, 1a exhibited LC dominated blue emission, under LE
excitation (355 nm). As the external pressure increased, 1a
presented constant uorescence reduction and phosphores-
cence enhancement. The intensity of the LE phosphorescence
showed exponential growth and was greatly increased: 12 times
and S15, ESI†). The absorption bands of 1a at about 290 and
40 nm can be attributed to ligand-centred (LC) transition. The
3
variable-excitation wavelength PL spectra of 1a at rt were
remarkably different from those of the proligand (Fig. S16 and
S17, ESI†). As shown in Fig. S18 (ESI†), 1a has low-energy (LE)
dominated dual emission bands at about 400 nm (high-energy,
HE band) and 680 nm (LE band) with a large LE/HE intensity
ratio of 100 (lex ¼ 280 nm). The HE band was consistent with
the solid emission of the proligand in both emission energy and
band prole, which can be assigned as a LC uorescence. The
LE band intensity was signicantly larger compared with that of
the proligand, and it remained at a certain strength even under
LE excitation (i.e., lex ¼ 360 nm), indicating that the LE band
was not limited to the emission of the proligand. Upon
increasing the excitation energy, the emission colour changed
from blue-white to red (Fig. S18b, ESI†) in the CIE-1931 chro-
maticity diagram.
Upon cooling to 200 K or a lower temperature, 1a showed
a new broad emission band at 560 nm, whose emission energy
was temperature-independent (Fig. S20a, ESI†). To better
understand the steady state PL, density functional theory (DFT)
and time-dependent density functional theory (TDDFT) calcu-
lations were conducted and the calculations based on singlet
monomeric 1a geometry revealed that the low-lying singlet
excited states were mainly localized on the Cz moieties, until the
metal-to-ligand charge transfer (MLCT) character became
ꢀ4
stronger at 2.23 GPa than that at 1 atm (10 GPa), whereas the
HE emission intensity was slightly weakened, resulting in
a remarkable colour change from weak blue to bright pink
(
Fig. 1b and c). Such PIPE is rare in the piezochromic lumi-
nescent materials. When the pressure was greater than
.23 GPa, the emission intensity decreased linearly (Fig. 1d, e
2
and S24, ESI†). The reduced LE emission and enhanced HE
emission recorded during a pressure relief process from
2
.28 GPa to 0 GPa (Fig. 2) indicated that the PIPE phenomenon
of 1a was reversible. To further explain these results, TDDFT
calculations were performed based on the T geometry of 1a at 1
atm and 2.5 GPa (Fig. S28–S30, ESI†). Under ambient condi-
1
3
1
tions, the T state was mainly composed of LC transition of Cz
moieties (79%) and LLCT (ligand-to-ligand charge transfer)
transition of Cu –Cz (9%). Pressurizing 1a to 2.5 GPa, the
3
3
3
MLCT/ LLCT transition became dominant in the T state
65%) while the percentage of LC transition of Cz moieties was
1
3
(
reduced to 14%. In addition, when the pressure increased from
atm to 2.5 GPa, the Cu contribution in the MLCT increased
from 6.46% to 11.75%. These computational results indicated
the external pressure strength of the Cu –Cz interactions,
1
3
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3
3
ꢀ
resulting in the increase of the MLCT/ LLCT contribution in of 3.756(3) A at 298 K (Fig. 3a). In addition, the Cz motifs
the excited state. Combining the crystal structure analysis and adopted a J-type aggregation along the a-axis, whereby the two
the computational results, it can be postulated that the weak LE adjacent Cz groups tightly stacked through p–p interactions
emission band is attributed to MSLC phosphorescence due to with an intermolecular Cz/Cz plane-to-plane distance (dCz/Cz
)
ꢀ
the rather weak Cu
3
–Cz interactions and the negligible Cu of about 3.480 A (Fig. 3a). 1b presented different intensity ratios
contribution to the MLCT state at ambient conditions. When of higher and lower absorption bands in UV-vis absorption
the pressure was increased to 2.23 GPa, the intensity of the LE compared with that of 1a, which explained the different crystal
phosphorescence was greatly enhanced, which could reason- colours of 1a and 1b (Fig. S12 and S13, ESI†). In sharp contrast,
ably be attributed to a cooperative effect between heavy-atom 1b shows HE dominated dual emission with a much smaller LE/
effects and MLCT promotion because of the shortening of HE intensity ratio of 1.25 (lex ¼ 280 nm) than that of 1a
dCu3/Cz as well as the signicant increase of Cu –Cz interac- (Fig. S19a, ESI†). The HE structured bands in the range of 350–
3
tions and Cu contribution in the MLCT (Fig. 4a).
In contrast, the Cu units in 1b packed as a stair-step innite S17, ESI†) which can be attributed to the LC emission upon LE
chain with one pair of weak intertrimer Cu/Cu interactions excitation (i.e., lex ¼ 360 nm). The excitation wavelength-
with a relatively long intermolecular Cu/Cu distance (dCu/Cu dependent emission colour changes were also found for 1b
Fig. S19b, ESI†). The DFT and TDDFT calculations revealed that
500 nm were similar to those for the proligand (Fig. S16 and
3
)
(
the low-lying singlet excited states were Cz localized, conrming
1
the LC feature of the HE emission of 1b. Both the lowest triplet
3
states of monomeric and dimeric 1b were a LC feature (Table
S6, ESI†), therefore the LE emission band of 1b can be attrib-
uted to the MSLC phosphorescence which experiences the ISC
1
3
from the MLCT state to the MLCT state and the internal
conversion (IC) of the triplet state. Such a proposed photo-
physical mechanism has been commonly observed in other CTC
44
systems. Because of the well-ordered J-type aggregation of the
Cz motifs, 1b exhibited aggregate/excimer emission with a lower
energy in the solid state, which further supported the lower
energy broad emission of 1b compared to that of the proligand.
Combining the experimental and computational studies, 1a
showed phosphorescence dominated emission, but 1b featured
similar emission behaviours to the proligand, revealing that the
stacking mode of the organic chromophore in the crystals
would be an essential factor for determining the PL properties
of the metal–organic complex.
Upon external pressure, the PL of 1b showed a continuous
red shi, accompanied by two-step changes including emission
enhancement (0.01–3.62 GPa) and emission reduction (3.62–
1
7.96 GPa) under 355 nm excitation (Fig. 3b–d). These obser-
vations were similar to the piezoluminochromism of pure Cz
ref. 40) and agreed well with the previously mentioned
(
suggestion for the Cz-centred characteristic luminescence of 1b.
Interestingly, both PL energy and intensity (or the integrated
area in Fig. S25, ESI†) showed a linear relationship versus the
external pressure as shown in Fig. 3e and f, respectively. The
emission spectra and photographs taken during the decom-
pression process indicate that the piezoluminochromic
phenomena of 1b (Fig. S26, ESI†) was reversible. The pressure-
dependent structural simulations and frontier molecular
orbital (FMO) analysis (Fig. S30–S34, ESI†) of 1b revealed that
the dCz/Cz was the only structural parameter to change
consistently with the cell volume change. It is a key factor that
inuences the overlap of molecular orbitals participating in the
PL transition, leading to a continuous bathochromic shi in the
Fig. 3 (a) The crystal packing of 1b at 298 K, showing the infinite chain
stacking model of Cz and Cu . The emission spectra of 1b at a range of
external pressures from (b) 0.01–3.20 GPa and (c) 3.62–17.96 GPa at
an excitation wavelength of 355 nm. (d) PL photographs of the 1b
crystal under compression up to 15.90 GPa. Linear fitting of the
external pressure and (e) PL energy and (f) PL intensity of 1b.
3
PL energy. As the Cz groups were well separated from the Cu
3
moieties with non-conjugated n-butyl chains and well packed to
form an innite and column-like Cz aggregator via p–p inter-
actions in the crystals, 1b mainly exhibited the Cz/Cz excimer-
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and MLCT promotion. The excellent responses to pressure of 1a
and 1b make them promising materials for use as pressure
sensors or in pressure detection.
Experimental section
Materials
All starting materials were purchased from commercial sources
and used as received without further purication. Detailed
characterization methods are included in the ESI.†
Synthesis of the 9-(4-(3,5-dimethyl-1H-pyrazol-4-yl)butyl)-
carbazole ligand (HL). Carbazole (10.32 g) was dissolved in
100 mL of toluene, and the solution was added to 1,4-dibro-
mobutane (118.2 g, 547.4 mmol) and tetrabutylammonium
bromide (TBAB, 2 g) in a 500 mL round bottom ask, and then
1
00 mL of 50% sodium hydroxide solution was added into the
ꢂ
mixed solution, and the stirring was continued at 45 C for 24 h.
The mixed solution was extracted with dichloromethane, the
extraction solvent was then steamed and placed under a fume
hood and allowed to volatilize for a week. Aer evaporation to
dryness, the blue solid obtained was separated and puried by
column chromatography to obtain a large amount of a white
Fig. 4 A schematic diagram of the (a) pressure-induced phospho-
rescence enhancement of 1a, and (b) the piezochromism of 1b. The
dominant luminescent components are highlighted.
solid, which was intermediate HL-1: 9-(4-bromobutyl)-9H-
1
carbazole with a yield of about 86%. H-NMR (400 MHz, CD
2
Cl
2
)
d 8.16 (d, J ¼ 7.8 Hz, 1H), 7.50 (m, 2H), 7.28 (dd, J ¼ 7.9, 6.8 Hz,
1
1
H), 4.39 (t, J ¼ 7.2 Hz, 1H), 3.44 (t, J ¼ 6.5 Hz, 1H), 2.07 (m, 1H),
based luminescence and the contribution of MLCT to the PL
13
1
0
2 2
.95 (m, 1H) ppm. C-NMR (400 MHz, CD Cl ) d 140.3, 125.7,
were negligible (Fig. 4b), and which are not favoured for d -
39
122.8, 120.3, 118.9, 108.7, 42.2, 33.4, 30.4, 27.6 ppm. Elemental
analysis for C H BrN, calcd (%): C 63.59, H 5.34, N 4.62; found
metal CTCs.
1
6
16
(%): C 64.07, H 5.63, N 4.58.
The eluent selected was dichloromethane : petroleum ether
1 : 8). Next K CO (80 mol, 11.04 g), acetylacetone (60 mmol, 6
2 3
Conclusions
(
In summary, a new piezochromic material, carbazole-based mL), and a small amount of 18-crown-6 was added to a three-
Cu(I) CTCs, consisting of a carbazole chromophore and necked round bottom ask containing 100 mL of acetone.
Cu Pz functional moieties linked by a non-conjugated alkyl Then 1-bromobutyl 4-oxazole (20 mmol, 6.038 g) was dissolved
3 3
chain, was designed. Signicant stacking conformations were in 60 mL of acetone and placed in a dropping funnel and
observed in the two crystalline polymorphs of 1a and 1b: attached to a three-necked ask. Aer installing the device,
discrete Cu –Cz adducts via p-acid/base interactions were nitrogen gas was added and the mixture was stirred at rt for
3
ꢂ
found in 1a, whereas the innite p–p stacking of Cz groups and 30 min. Aer 30 min, the temperature was raised to 50 C, and
3
a stair-step innite chain of Cu motifs were obtained in 1b. the 1-bromobutyl 4-oxazole solution in the dropping funnel was
Like pure carbazole molecules, upon increasing the external gradually added dropwise to the three-necked ask, and the
pressure, the emission maximum of 1b gradually red-shied mixture was heated to reux, and the nitrogen was le owing
and the intensity of the uorescence band slightly increased for 17 h. Aer the reaction was completed, distilled water was
before gradually decreasing. However, the unprecedented added, and the mixture was extracted with a dichloromethane
phenomenon of the pressure-induced phosphorescence solution, and then steamed, and puried by column chroma-
enhancement (PIPE) of 1a was discovered, which was a rare case tography. The eluent selected was dichloromethane : petroleum
in the eld of piezochromic luminescence. Theoretical and ether (1 : 10) and colorless needle-like crystals were obtained,
experimental investigations illustrated that the increase of the which was the intermediate HL-2: 3-(4-(9H-carbazol-9-yl)butyl)
1
LE phosphorescence band intensity originated from the Cu
excimer in 1a. External heavy atom effects induced MSLC MHz, CD
phosphorescence and then promoted MLCT events from the ¼ 7.4, 6.9 Hz, 1H), 4.35 (t, J ¼ 7.2 Hz, 1H), 3.58 (t, J ¼ 7.1 Hz, 1H),
3
–Cz pentane-2,4-dione with a yield of about 51%. H-NMR (400
2
Cl
2
) d 8.13 (d, J ¼ 7.8 Hz, 1H), 7.48 (m, 2H), 7.26 (dd, J
1
3
Cu
3
unit to the Cz groups cooperatively contributed to the 2.12 (m, 3H), 1.92 (m, 1H), 1.84 (m, 1H), 1.35 (m, 1H) ppm. C-
enhancement of the LE phosphorescence band from 1 atm to NMR (400 MHz, CD Cl ) d 204.0, 140.4, 125.6, 122.7, 120.2,
2
2
2
.5 GPa. These studies demonstrated a novel strategy for 118.8, 108.7, 68.1, 42.7, 29.2, 28.8, 27.8, 25.3 ppm. Elemental
designing a new class of piezochromic materials with PIPE analysis for C21 , calcd (%): C 78.47, H 7.21, N 4.36; found
properties via the combination of external heavy atom effects (%): C 78.67, H 7.40, N 4.37.
H23NO
2
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The diketone intermediate was added to a ask containing then anisotropically. All the hydrogen atoms of the ligands were
hydrazine hydrate (80%, 14 mL), ethanol (100 mL), and kept at placed in calculated positions with xed isotropic thermal
ꢂ
7
0 C for 15 h, and the ethanol evaporated to give a yellow oil. parameters and included in the structure factor calculations in
Aer freezing in a refrigerator for one week, the yellow oil was the nal stage of the full-matrix least-squares renement.
taken out, and a white solid was observed. Aer washing with For 1b, the low quality of the crystal structure of the sample
a diethyl ether solution, it was ltered and dried to give was due to poor data and a disorder problem of the exible n-
product HL [9-(4-(3,5-dimethyl-1H-pyrazol-4-yl)butyl)-9H- butyl chain and the carbazole ring, respectively. The cell
a
1
carbazole] with a yield of about 39%. H-NMR (400 MHz, parameters and atomic position of the CTC rings and heavy
CD Cl
.7, 1H), 4.35 (t, J ¼ 7.2 Hz, 1H), 2.38 (t, J ¼ 7.6 Hz, 1H), 2.13 (s, method.
2
2
) d 8.13 (d, J ¼ 7.8 Hz, 1H), 7.50 (m, 2H), 7.25 (dd, J ¼ 7.9, atom were generated from the SCXRD data by the Patterson
6
3
1
3
H), 1.90 (m, 1H), 1.56 (m, 1H) ppm. C-NMR (400 MHz,
All the calculations were performed using the system of
46,47
CD Cl ) d 141.8, 140.4, 125.6, 122.7, 120.2, 118.7, 115.0, 108.7, computer programs.
The crystal data and structure rene-
3.0, 28.7, 28.2, 22.8, 10.6 ppm. IR spectrum (KBr, cm ): 3203 ment parameters are summarized in Table S1 (ESI†). Selected
w), 3147 (w), 3089 (w), 3042 (w), 3007 (w), 2928 (m), 2856 (w), bond lengths and angles are given in Table S2 (ESI†).
626 (m), 1592 (m), 1482 (m), 1451 (m), 1413 (m), 1383 (w), 1325
m), 1298 (w), 1238 (m), 1206 (m), 1177 (w), 1153 (m), 1104 (w),
2
2
ꢀ
1
4
(
1
(
1
7
Conflicts of interest
066 (w), 1020 (w), 1000 (w), 924 (w), 901 (w), 850 (w), 771 (w),
49 (s), 721 (s), 628 (w), 615 (w), 556 (w), 527 (w), 445 (w), 421 There are no conicts to declare.
(m). Elemental analysis for C H N , calcd (%): C 79.46, H
21 23 3
7
.30, N 13.24; found (%): C 79.61, H 7.41, N 13.41. Detailed
Acknowledgements
characterization of HL and the intermediates are included in
the ESI.†
This work was supported by the National Natural Science
Foundation of China (no. 21731002, 21725304, 21975104, and
21901085), the Guangdong Major Project of Basic and Applied
Research (2019B030302009), and the high-performance public
computing service platform of Jinan University. G.-H. Ning
thanks the Guangdong Basic and Applied Basic Research
Foundation (2019B151502024), the Guangdong Province Pearl
River Scholar Funded Scheme (2019), and the Fundamental
Research Funds for the Central Universities (21619315) for their
Synthesis of 1a
45
A solvo thermal method was used to synthesize the target
complex 1a and 1b. The Cu O (4.32 mg, 0.03 mmol), HL
9.51 mg, 0.03 mmol), 1.5 mL of ethanol and 1.5 mL of water
2
(
were added to a hard glass tube with an inner diameter of 8 mm,
and the tube was sealed and heated to 140 C for 72 h. Aer
cooling the tube and its contents to rt at a rate of 3 C per h, the
contents were ltered and washed with ethanol to give a light
ꢂ
ꢂ

nancial support.
yellow block crystal with a yield of about 52%. Elemental anal-
ysis for C63
H
66
N
9
Cu
3
, calcd (%): C 66.15, H 6.06, N 10.74; found Notes and references
(%): C 66.38, H 5.84, N 11.06.
1
2
3
4
5
A. J. McConnell, C. S. Wood, P. P. Neelakandan and
J. R. Nitschke, Chem. Rev., 2015, 115, 7729–7793.
P. Theato, B. S. Sumerlin, R. K. O'Reilly and T. H. Epps III,
Chem. Soc. Rev., 2013, 42, 7055–7056.
Synthesis of 1b
The Cu O (4.22 mg, 0.03 mmol), HL (9.51 mg, 0.03 mmol) and
2
3
mL of ethanol were added to a hard glass tube with an inner
Z. Fu, K. Wang and B. Zou, Chin. Chem. Lett., 2019, 30, 1883–
ꢂ
diameter of 8 mm, and the tube was sealed and heated to 140 C
1894.
for 72 h. Aer cooling the tube and its contents to rt at a rate of
L. Bai, P. Bose, Q. Gao, Y. Li, R. Ganguly and Y. Zhao, J. Am.
Chem. Soc., 2016, 139, 436–441.
T. Ono, Y. Tsukiyama, A. Taema, H. Sato, H. Kiyooka,
Y. Yamaguchi, A. Nagahashi, M. Nishiyama, Y. Akahama,
Y. Ozawa, M. Abe and Y. Hisaeda, ChemPhotoChem, 2018,
ꢂ
3
C per h, the contents were then ltered and washed with
ethanol to give a colorless lamentous crystal with a yield of
about 70%. Elemental analysis for C H N Cu , calcd (%): C
6
3
66
9
3
66.38, H 5.84, N 11.06; found (%): C 66.12, H 5.65, N 10.96.
2
, 416–420.
Crystallographic studies
6
H. Yan, F. Yang, D. Pan, Y. Lin, J. N. Hohman, D. Solis-Ibarra,
F. H. Li, J. E. P. Dahl, R. M. K. Carlson, B. A. Tkachenko,
A. A. Fokin, P. R. Schreiner, G. Galli, W. L. Mao, Z. X. Shen
and N. A. Melosh, Nature, 2018, 554, 505–510.
7 Y. Gu, H. Liu, R. Qiu, Z. Liu, C. Wang, T. Katsura, H. Zhang,
M. Wu, M. Yao, H. Zheng, K. Li, Y. Wang, K. Wang, B. Yang,
Y. Ma and B. Zou, J. Phys. Chem. Lett., 2019, 10, 5557–5562.
8 Q. Li, Z. Chen, B. Yang, L. Tan, B. Xu, J. Han, Y. Zhao, J. Tang
and Z. Quan, J. Am. Chem. Soc., 2020, 142, 1786–1791.
9 M. S. Kwon, J. Gierschner, J. Seo and S. Y. Park, J. Mater.
Chem. C, 2014, 2, 2552.
Single-crystal X-ray diffraction (SCXRD) data for 1a and 1b were
collected by an Cryostream system (Oxford Cryosystems) on
a XtaLAB PRO MM007 DW diffractometer system equipped with
a RA-Micro7HF-MR-DW(Cu/Mo) X-ray generator and a Pila-
ꢀ
tus3R-200K-A detector (Rigaku, Japan), Cu Ka, l ¼ 1.54178 A.
The numerical absorption corrections were applied using the
ABSCOR program. The data set temperatures were 296 K and
100 K for 1a and 298 K for 1b. For 1a, the structures were solved
using direct methods, which yielded the positions of all the
non-hydrogen atoms. These were rst rened isotropically and
4430 | Chem. Sci., 2021, 12, 4425–4431
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Chemical Science
1
1
0 A. Pucci, Sensors, 2019, 19, 4969.
1 D. A. Davis, A. Hamilton, J. Yang, L. D. Cremar, D. Van
28 J. Zheng, Z. Lu, K. Wu, G.-H. Ning and D. Li, Chem. Rev.,
2020, 120, 9675–9742.
Gough, S. L. Potisek, M. T. Ong, P. V. Braun, 29 J. Zheng, H. Yang, M. Xie and D. Li, Chem. Commun., 2019,
T. J. Mart ´ı nez, S. R. White, J. S. Moore and N. R. Sottos,
Nature, 2009, 459, 68–72.
55, 7134–7146.
30 Q. Li and Z. Li, Acc. Chem. Res., 2020, 53, 962–973.
12 J. W. Chung, Y. You, H. S. Huh, B.-K. An, S.-J. Yoon, 31 C. H. Woodall, S. Fuertes, C. M. Beavers, L. E. Hatcher,
S. H. Kim, S. W. Lee and S. Y. Park, J. Am. Chem. Soc.,
009, 131, 8163–8172.
3 Y. Wang, X. Tan, Y.-M. Zhang, S. Zhu, I. Zhang, B. Yu,
K. Wang, B. Yang, M. Li, B. Zou and S. X.-A. Zhang, J. Am.
Chem. Soc., 2015, 137, 931–939.
A. Parlett, H. J. Shepherd, J. Christensen, S. J. Teat,
M. Intissar, A. Rodrigue-Witchel, Y. Suffren, C. Reber,
C. H. Hendon, D. Tiana, A. Walsh and P. R. Raithby,
Chem.–Eur. J., 2014, 20, 16933–16942.
2
1
32 X.-C. Shan, F.-L. Jiang, D.-Q. Yuan, H.-B. Zhang, M.-Y. Wu,
L. Chen, J. Wei, S.-Q. Zhang, J. Pan and M.-C. Hong, Chem.
Sci., 2013, 4, 1484–1489.
1
1
1
4 J. Kunzelman, M. Kinami, B. R. Crenshaw, J. D. Protasiewicz
and C. Weder, Adv. Mater., 2008, 20, 119–122.
5 B. S. Li, X. D. Wen, R. P. Li, Z. W. Wang, P. G. Clem and 33 S.-Z. Zhan, M. Li, X.-P. Zhou, J.-H. Wang, J.-R. Yang and D. Li,
H. Y. Fan, Nat. Commun., 2014, 5, 1–7. Chem. Commun., 2011, 47, 12441–12443.
6 W. Z. Yuan, Y. Tan, Y. Gong, P. Lu, J. W. Y. Lam, X. Y. Shen, 34 J.-H. Wang, M. Li, J. Zheng, X.-C. Huang and D. Li, Chem.
C. Feng, H. H.-Y. Sung, Y. Lu, I. D. Williams, J. Z. Sun,
Y. Zhang and B. Z. Tang, Adv. Mater., 2013, 25, 2837–2843.
7 S. Bergantin, M. Moret, G. Buth and F. P. A. Fabbiani, J. Phys.
Chem. C, 2014, 118, 13476–13483.
8 Q. Qi, J. Qian, X. Tan, J. Zhang, L. Wang, B. Xu, B. Zou and
W. Tian, Adv. Funct. Mater., 2015, 25, 4005–4010.
Commun., 2014, 50, 9115–9118.
35 W.-X. Ni, M. Li, J. Zheng, S.-Z. Zhan, Y.-M. Qiu, S. W. Ng and
D. Li, Angew. Chem., Int. Ed., 2013, 52, 13472–13476.
36 R. Galassi, M. A. Rawashdeh-Omary, H. V. R. Dias and
M. A. Omary, Comments Inorg. Chem., 2019, 39, 287–348.
37 O. Elbjeirami, M. D. Rashdan, V. Nesterov and
M. A. Rawashdeh-Omary, Dalton Trans., 2010, 39, 9465.
1
1
1
9 N. Li, Y. Gu, Y. Chen, L. Zhang, Q. Zeng, T. Geng, L. Wu,
L. Jiang, G. Xiao, K. Wang and B. Zou, J. Phys. Chem. C, 38 S.-Z. Zhan, F. Ding, X.-W. Liu, G.-H. Zhang, J. Zheng and
019, 123, 6763–6767. D. Li, Inorg. Chem., 2019, 58, 12516–12520.
0 H. Liu, Y. Gu, Y. Dai, K. Wang, S. Zhang, G. Chen, B. Zou and 39 L.-R. Xing, Z. Lu, M. Li, J. Zheng and D. Li, J. Phys. Chem.
B. Yang, J. Am. Chem. Soc., 2020, 142, 1153–1158. Lett., 2020, 11, 2067–2073.
1 Y. Liu, Q. Zeng, B. Zou, Y. Liu, B. Xu and W. Tian, Angew. 40 Y. Gu, K. Wang, Y. Dai, G. Xiao, Y. Ma, Y. Qiao and B. Zou, J.
Chem., Int. Ed., 2018, 57, 15670–15674. Phys. Chem. Lett., 2017, 8, 4191–4196.
2 X. Sun, X. Wang, W. Liang, C. Gao, Z. Sui, M. Liu, R. Dai, 41 M. M. Olmstead, F. Jiang, S. Attar and A. L. Balch, J. Am.
2
2
2
2
Z. Wang, X. Zheng and Z. Zhang, J. Phys. Chem. C, 2018,
22, 15861–15867.
3 K. Nagura, S. Saito, H. Yusa, H. Yamawaki, H. Fujihisa,
Chem. Soc., 2001, 123, 3260–3267.
42 H. V. Rasika Dias and C. S. Palehepitiya Gamage, Angew.
Chem., Int. Ed., 2007, 46, 2192–2194.
1
2
H. Sato, Y. Shimoikeda and S. Yamaguchi, J. Am. Chem. 43 P. F. McMillan, Chem. Commun., 2003, 8, 919–923.
Soc., 2013, 135, 10322–10325.
4 B. Xu, Y. Mu, Z. Mao, Z. Xie, H. Wu, Y. Zhang, C. Jin, Z. Chi,
44 L. D. Earl, J. K. Nagle and M. O. Wolf, Inorg. Chem., 2014, 53,
7106–7117.
2
S. Liu, J. Xu, Y.-C. Wu, P.-Y. Lu, A. Lien and M. R. Bryce, 45 R.-J. Wei, H.-G. Zhou, Z.-Y. Zhang, G.-H. Ning and D. Li, CCS
Chem. Sci., 2016, 7, 2201–2206. Chem., 2020, 2, 2045–2053.
5 Y. Gong, S. He, Y. Li, Z. Li, Q. Liao, Y. Gu, J. Wang, B. Zou, 46 C. B. H u¨ bschle, G. M. Sheldrick and B. Dittrich, J. Appl.
Q. Li and Z. Li, Adv. Opt. Mater., 2020, 8, 1902036. Crystallogr., 2011, 44, 1281–1284.
6 L. Huang, C. Qian and Z. Ma, Chem.–Eur. J., 2020, 26, 11914– 47 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
1930. 2008, 64, 112–122.
7 J. Yang, M. Fang and Z. Li, InfoMat, 2020, 2, 791–806.
2
2
2
1
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2021 The Author(s). Published by the Royal Society of Chemistry
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